This invention relates to ultrasonic interrogation and, more particularly, to a mechanical ultrasonic scanner of the type typically used in medical diagnosis.
Mechanical ultrasonic sector scanners are commonly used in medical diagnosis. Such a scanner has in a hand held housing an ultrasonic transducer that rotates or oscillates to transmit ultrasonic energy to a sectorial area and receive echos therefrom. A signal representative of the received echoes modulates the beam of a cathode ray tube. The beam is controlled to represent on the screen the sector being scanned. As a result, the cathode ray tube displays an image of the scanned sector, which can be used for medical diagnosis when parts of the human body are interrogated by the scanner.
Numerous arrangements have been devised to drive an ultrasonic transducer mechanically so as to effect a sector scan. For example, Matzuk U.S. Pat. No. 4,092,867 discloses an ultrasonic transducer secured to a permanent magnet. The transducer and magnet are mounted for rotation between a pair of magnetic armature poles around which a pair of servo drive coils are wound. The coils are connected to the output of a servo amplifier to which a signal representative of the angular position of the ultrasonic transducer and a signal representative of the desired angular position are applied.
Connell et al U.S. Pat. No. 4,149,419 discloses a rotor on which four ultrasonic transducers are mounted at 90 degree intervals. The rotor is continuously driven by a motor about an axis perpendicular to the axis of rotation of the motor shaft and the transducers are individually activated as they pass through a given sector of each rotor revolution.
Paton et al U.S. Pat. No. 4,120,291 discloses an ultrasonic probe, pivotally attached at one end to the periphery of a continuously rotating crank. The other end of the probe at which an ultrasonically active surface is disposed is secured to a scanner housing by a rolling diaphragm. The probe is constrained by a pair of plates to move in a single plane so as to oscillate back and forth in the plane as the crank rotates.
The number of frames per second of visually displayed data that can be collected by a mechanical sector scanner depends upon the motor load including the moment of inertia of the rotating or oscillating transducer assembly connected to the motor. If the load becomes too great, perceptible vibration occurs, which degrades the image displayed by the CRT. Thus an important characteristic of a mechanical sector scanner is a small moment of inertia. Another desirable characteristic is compactness of component layout within the housing.